Just a random thought but would a DiSEqC switch work for connecting two 1090Mhz antennas to one feed line or does it need the 22kHz signal up the wire?
I believe a Diseqc switch needs the 22kHz signal to switch between inputs, I doubt it can be used to combine feeds if that’s what you’re looking for.
I used one of these combiners to allow two system to share one antenna, for testing. There is no reason you couldn’t use it to combine two antenna to one system.
I am not aware of full details of DiSEqC switches.
My logical conclusion from it’s name is:
As the name suggests, it is a “switch” , not a “combiner”. If you have antenna A & antenna B, it will switch between A & B. as a result at any time only A or only B will be connected to receiver, and NOT A+B connected to receiver.
Well above is only logic, which may be wrong. Fact can be told by those who have used it or are aware of it’s details.
A farmer sent his son to a university. After 4 years, the son completed his education and finally returned to his village. Next morning on the breakfast table, the farmer asked his son “You have spent 4 years of your life and I have spent a lot of money on your education, what have you learned”. The son said “logic”. Farmer asked “what is it’s use”. son said I can prove things by it, for example I can prove that this egg on the table is actually 2 eggs. The son then presented his logic and proved that there were 2 eggs on the table. The farmer smiled, ate the egg and said to his son “you eat the second egg”. 
Miracle of logic 